Among the many environmental problems which mankind faces in the 21st century is the problem of environmental sustainability and management of the tremendous amount of generated polymer waste. Among various polymer wastes, the management of used tires and rubber waste and crosslinked plastics is a major environmental problem requiring an efficient solution. The present invention is specifically directed toward the creation of a new, environmentally friendly ultrasonic single screw and twin screw extrusion apparatus and processes for the recycling of used tires and rubber waste and crosslinked plastics. An extensive research was conducted to understand various parameters of the process and mechanisms and models of rubber devulcanization using a single screw extruder process. This research culminated in the issuance of number of patents and multiple scientific publications in scientific journals and books. Because of these successful efforts the application of the high power ultrasound in the single screw extrusion process for breaking down the rubber network with the purpose of recycling is an established field of study around the world. Though it is a topic of study, the apparatus and processes can still benefit from additional discoveries and developments, such as those disclosed herein.
Notably, to the extent ultrasound has been incorporated into twin screw extruder processes, the ultrasound horn is taught as being placed at the exit of the die of the extruder, as in U.S. Pat. No. 5,284,625. To the extent ultrasound has been incorporated into the single screw extruder process, the ultrasound horn has been placed at the exit of the die of the extruder, as in the aforementioned U.S. Pat. No. 5,284,625. Ultrasound horns have also been placed within the barrel of single screw extruders, as in U.S. Pat. No. 6,095,440, which teaches providing a special helical channel in the barrel and placing the distal end of the horn in this helical channel. The horn is square in cross section and has an arced channel defined at its distal end, the channel extending from one corner of the square to the opposite corner. This is seen as being an undesirable horn design, but is needed to permit the horn to communicate with the special helical channel. These patents teach the devulcanization of rubber in these extruders.
Yet other single screw extruders have been modified to include ultrasound horns within the die, as in European Patent Application No. 1645381, which teaches using such extruders for the purpose of improving properties in molding a resin material. U.S. Patent Application No. 2009/0275689 has also taught placing the ultrasonic horn at the barrel, but for the purpose of dispersing materials in polymers.
The present invention focuses upon the reclaiming of plastics and rubber by the devulcanization of vulcanized rubber and the decrosslinking of crosslinked plastic in single and twin screw extruders, wherein one or more ultrasonic horns are placed at the barrel of the single and twin screw extruders, with a particular flow path provided at the horn.